(1) Field of the Invention
The present invention relates to a plasma display panel (PDP) and a method for restoring the function of a PDP, when it becomes deteriorated, the PDP being capable of being used as the display of wall-hanging color televisions and a variety of other information display devices for the reason that PDP is inexpensive to produce and is thin with a large, high-resolution screen.
(2) Description of the Related Art
Plasma display panels (hereinafter referred to also as PDP(s)) are roughly categorized into AC type and DC type in terms of their drive methods, whereas they are roughly divided into surface discharge type and counter discharge type in terms of their discharge methods. Nowadays, AC surface discharge PDPs are in the mainstream because PDPs of this type can have a high-definition screen and allow for easy and simple production. An attempt has been made to improve viewability and color reproducibility of the PDPs by increasing the luminance of display that utilizes phosphors.
For example, conventional PDPs include a technology in which phosphor layers are composed of a large number of granular phosphors, each being coated with a thin film made of translucent material whose refractive index is smaller than that of the phosphors (see Japanese Laid-Open Patent publication No. 7-320645). This conventional PDP is capable of producing the following effects: the display luminance is increased thanks to the improvement in the excitation efficiency, which is attributable to the fact that the reflection at the surface layer of the phosphors is reduced and that the transmittance of ultraviolet (UV) light into the phosphors is increased; and the decay of the phosphors can be prevented because the thin-films protect the phosphors from ions at the time of plasma discharge.
Meanwhile, for an AC-driven PDP, which uses a magnesium oxide film as a dielectric protective film, a PDP is known that prevents the degradation of electric characteristics by forming, on the magnesium oxide film, an anti-gas-absorbing film having an insulating property and a visible-light transmission property so as to prevent the magnesium oxide film from absorbing gas at the fabrication stage (see Japanese Laid-Open Patent publication No. 2000-348626). Since this PDP is capable of reducing the gas absorption of magnesium oxide as well as reducing the breakdown voltage by successively forming an anti-gas-absorbing film on the magnesium oxide film, it is possible to achieve the enhanced stability and improved performance of discharge.
Furthermore, there has been proposed a PDP fabrication method that includes a process in which: electrodes, which are formed on at least one of a pair of glass substrates, are covered with a dielectric layer; a protective layer for protecting such dielectric layer from discharge and a temporary protective film for temporarily protecting the surface of such protective film up until the panel assembling process, are formed on the surface of such dielectric layer; and after the one glass substrate and the other substrate are assembled into a panel, the temporary protective film is removed by generating plasma in the panel (see Japanese Patent No. 3073451). In this fabrication method, since the temporary protective film is successively formed on the protective film after such protective film is formed, no affected layer is formed on the surface of the protective film. Accordingly, it becomes possible for the plasma display panel to have a protective film with excellent discharge properties.
Meanwhile, it is known that wavelength shift and luminance degradation of phosphors occur when a PDP is sealed in the fabrication and assembling processes or after being used for a long period of time as a product. Such wavelength shift and luminance degradation are especially notable in blue phosphors out of the three color phosphors. In the case of wavelength shift, discoloration of luminescent colors occurs, whereas in the case of luminance degradation, luminescence intensity is reduced, both of which lead to the deterioration in display function.
Such deterioration in the display function of PDPs is assumed to occur because of one of the following factors: wavelength shift that occurs due to the OH group being bound to BAM (blue phosphor: an abbreviation of BaMgAl 10O17) as a result of oxygen defect and luminance degradation due to the oxidization of EU2+; and destruction of BAM structure due to (UV) light, i.e., due to lowered crystallinity. However, no proposal has been made about means for restoring a deteriorated display function of PDPs attributable to the above wavelength shift and luminance degradation.
The present invention has been conceived in view of the above conventional problem, and it is an object of the present invention to provide a method for restoring the function of a plasma display panel that can efficiently restore the display function of a plasma display panel when its display function is deteriorated due to wavelength shift and luminance degradation of phosphors, as well as to provide a plasma display panel that is equipped with means for efficiently restoring its deteriorated display function.